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BIOLOGY 

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LIBRARY 


Inn-  re/inn  ft 'I  j'mm  Cailiard's    Medical 

Journal,  _      hy  >,,,  m 

•    in    tli,    /,rnj, 


MBTH  <'tBccum»s    IN    THK  EMBBYO:    PLAO 

FFLE  THE    Ax.UX"  IlESPIKAT 

BKPIRATIOX    ix    THK    XEW-BOBX  :    THE    CHANGE   is  MECHAXICS   wmcn   THB 

YI58  TO  THE   AlB-CHAUBEB  IX  THE  EGO. 
\I    Di   THE  TISSUES  Or  THE   WoMB.* 

Br    W.    H.    TKII'I.riT.    .V  I 


M 


seen  that  respiration  and  circulation  most  be  treated  together,  since 
i  a  connected  movement  for  pumping  the  commerce  in  and  through  the 
organism  for  elaborating  structure  and  evolving  force,  and  *****  the  whole  • 
founded  in  the  power  of  producing  rhythmical  changes  in  pressure,  the  fluids 
flowing  from  high  to  low  pressure  in  conformity  with  organic  law ;  that  the 
••stines  and  bloodTeasds  are  necessarily  allied  in  respiration  in  order 
to  make  importation  and  transportation  a  connected  movement  between  the 
ceD-timod  and  environment,  which  the  scheme  calk  for.     In  other  words,  that 
xstptM?  action  in  respiration  compel*  the  commerce  in  the  Teaauh,  while  the 
action  in  the  heart,  arteries  and  venous  system  circulates  it  through  the  organ 
the  action    being  unified   throughout   by  means  of  the    nerroas  com- 
binatians  in    the   medulla   oblongata,  in   which   the  respiratory,   raso-motor 
dontary  motor  centres,  are  correlated,  the  one  calling  for  the  other,  as  has 
folly  set  forth  in  the  preceding  pages,  and  that  the  vital  phenomena, 
:nical  and  physiological,  appertaining  to  respiration,  circulation  absorp- 
tion, etc.,  are  readily  explained  and  accounted  for,  giving  absolute  proof  of 
the  correctness  of  the  premises,  as  before  remarked.     We  now  follow  this 
matter  a  little  farther,  and  take  op 

CI BrrLATIOX   IX    THE   EXBBTO, 

a  subject  which,  it  most  be  admitted,  is  at  present  veiled  in  deep  obscurity. 
This  is  nevertheless  susceptible   of  ftrjJhmmtitw^     The  embryo  is  an  aquatic 


•"""  *  — — y  "•"*•  *-'~ri — I '  *~  r-"— "—  — •"**-*  "~- — T  ruiinnaij  if  tii 

Body :  or.  tfte  Xeehaoic*  in  Scepintjoo.  airrtrttM  Absorption.  Etc.,-  ehapun  zrt  Md  rrii. 


r 


:.  :   /.:"•:••/: : 

••  •   «  ;   •;  ... 


animal,  since  it  leads  a  subaquatic  existence,  being  placed  under  water  (Fig. 
1)  and  deeply  buried  in  the  maternal  tissues,  which  would  account  for  the 
peculiarities  that  obtain  in  its  circulation  approximating  it  to  the  stages  in  de- 
velopment represented  in  fishes  and  amphibia. 


FIG.  1. — GRAVID  HUMAN  UTERUS  AND  CONTENTS,  showing  the  relations  of  the  cord,  placenta, 
membranes,  etc.,  about  tbe  end  of  the  seventh  month.  1,  decidua  vera  ;  2,  decidua  reflexa  ; 
3,  chorion;  4,  amnion.  (After  Dalton.) 

The  physical  conditions  under  which  the  embryo  is  evolved  determine 
the  special  vascular  arrangements  for  effecting  circulation,  while  the  trans- 
formations which  accompany  this  provide  for  the  radical  physical  changes 
which  are  ushered  in  at  the  end  of  the  term,  when  it  becomes  an  air- 
breather,  the  fundamental  circumstance  underlying  it  all  being  an  adjustment 
ivith  pressure,  and  the  power  of  effecting  rapid  rhythmical  changes  in  pressure,  or 
of  producing  the  universal  pumping  actions  going  on  in  the  body.  For  ex- 
ample, we  have  seen  that  the  rhythmical  expansions  and  contractions  pervad- 
ing the  body  in  the  air-breather,  and  known  as  respiration,  compel  oxygen  and 
aliment  in  the  circulatory  apparatus  for  evolving  force  and  producing  growth ;  so, 
in  like  manner,  a  similar  necessity  exists  in  the  embryo  for  compelling  the  nutri- 
tive and  force-producing  elements  in  its  circulation  for  producing  growth  and 
evolving  force,  which  is  principally  expended  in  elaborating  its  structures. 
But  since  the  embryo  feeds  in  the  uterine  sinuses  from  which  the  com- 
merce is  obtained,  and  into  which  the  waste  products  are  returned,  this  calls 
for  the  differentiation  of  the  special  organ  known  as  the  placenta,  and  which 
answers  to  the  more  highly  differentiated  lungs  and  intestinal  canal  which  are  to 
substitute  it  at  the  end  of  the  intra-uterine  term  as  the  relative  adjustments  with 
the  larger  environment,  lower  pressure,  and  higher  order  and  amount  of  work 
which  this  involves.*  The  placental  souffle,  then,  which  is  distinctly  heard 
through  the  maternal  structures  is  the  analogue  of  respiration  in  the  air- 
breather,  the  relative  ratio  of  the  movements  to  the  pulsations  in  the  foetal  heart 

•For  further  particulars,   see  Part  II.   of  this  work,   "On  the  Relation  of  Gravitation  to 
Development,"  to  be  issued  shortly. 


being  also  the  same,  or  as  1  to  I  of  tin-  latter,  whilst  the  villi  are  the  analogues 
of  tilt*  villi  is  tin-  intestinal  canal,  tho  ono  1n'ing  submerged  in  the  sinuses,  the 
other  in  the  juices  in  the  intestine.  Since  the  pumping  action  in  respiration  is 
absolutely  es-ential  for  compelling  the  comineive  in  tin'  vessels,  it  follows  that 
this  circumstance  shmilil  l)o  represented  in  the  t>mbryo,\i8  the  maternal  blood 
(loos  not  enter  the  embryo,  the  latter  feeding  out  of  lEe  sinuses  simply  by 
menus  of  the  villi  in  the  pkoenta/and  tliis  pumping  action  spoken  of  ;  for  here, 
as  elsewhere  in  the  Ixxly.  there  are  no  means  for  increasing  circulation  but  by 
rlii/tliiiu'rtil  I'/HHt'ifx  in  fi-is.-iii-t'.  The  result  must  then  be  the  action  in  the 
plaeeiita  simulating  respiration.  The  relative  frequency  of  this  movement  to 
the  action  taking  place  in  the  f<etal  heart  is  as  1  to  4,  or  the  same  as  in  respira- 
tion. 

Tli i is.  in  the  case  of  the  placeutal  souffle  it  is  30  to  35,  and  in  the  foetal  heart 
tho  pulsations  are  from  120  to  140  per  minute ;  while,  in  the  case  of  the  air- 
breather,  the  pumping  action  in  the  trunk  or  respiration  is  from  16  to  20,  and 
in  the  heart  from  fiO  to  80  per  minute.  Again,  tliis  action  in  the  placenta 
servos  not  only  to  pump  the  tluids  in  and  out  of  the  sinuses,  but  at  the  same  time 
it  also  aspirates  tho  venous  blood  in  the  embryo  for  effecting  oxygenation  in  it 
the  same  as  obtains  in  the  lungs  :  the  heart  and  vessels  assisting  in  the  one  as 
well  as  in  the  other,  since  it  all  forms  a  connected  movement.  We  now  see  that  by 
reason  of  the  great  increase  in  pressure  that  obtains  in  the  embryo,  the  action 
in  the  organs  for  changing  pressure  is  materially  assisted,  since  the  fluids  flow 
more  readily  in  consequence.  And  here  comes  in  the  benefit  of  the 
amniotic  fluid,  which  not  only  increases  pressure  in  proportion,  but  at  the  same 
time  it  serves  to  transmit  the  force  in  the  placenta  and  uterine  walls  to  the 
emlirvo  for  compelling  corresponding  changes  in  pressure  upon  the  blood  in  con- 
nection with  the  special  functions. 

As  illustrating  this  fact,  .we  see  that  when  the  placenta  expands  for  aspirating 
the  tluids  in  the  uterine  sinuses,  the  organ  advances  into  the  uterine  cavity,  it 
swells  out  and  occupies  more  room,  and,  by  thus  encroaching  upon  the  embryonic 
area,  it  produces  corresponding  increase  in  pressure  upon  the  liquor  amnii  and 
omliryo,  with  low  pressure  in  itself,  which  fulfils  the  conditions  for  increasing  cir- 
culation from  the  embryo  to  the  placenta,  at  the  same  time,  that  it  should  aspi- 
rate the  fluid  in  the  uterine  sinuses.  It  could  not  do  otherwise  in  the 
very  nature  of  things.  During  contraction  in  the  placenta,  the  opposite 
conditions  should  obtain,  since  this  would  determine  high  pressure  in  the  latter 
with  low  pressure  in  the  embryo,  the  blood  in  consequence  flowing  through  the 
umbilical  vein  with  augmented  speed,  and  for  the  reason  that  contraction 
should  induce  the  volume  of  the  placenta,  which  would  inevitably  reduce 
pressure  in  the  embryo  in  proportion,  the  blood  flowing  from  one  into  the 
other  in  conformity  with  organic  law.  To  this,  again,  must  be  added  the 
action  in  the  heart  for  aspirating  the  blood  in  the  placenta.  The  media 
in  which  the  animal  lives  obviates  the  necessity  for  the  extensive  arrange- 
ments for  reducing  pressure  in  the  chest,  which  obtain  in  the  lighter  media 
of  the  atmosphere,  the  heart,  together  with  the  force  in  the  placenta  and 
umbilical  vein,  being  sufficient  for  the  purpose. 


A  subaquatic  existence  calls  for  but  slight  reduction  in  pressure  in 
order  to  compel  movement ;  accordingly,  we  have  the  blood  rushing  in  and 
out  of  the  heart  as  a  result  of  the  rhythmical  expansions  and  contractions  in  this 
organ  ;  while  for  increasing  this  action,  the  vessels  are  combined  in  the 
mechanics  by  means  of  the  vaso-motor  apparatus,  and  which,  undoubtedly,  con- 
nects with  the  action  in  the  placenta.  The  right  ventricle  is  thicker  and  stronger 
than  the  left,  as  adjustment  for  this  mechanics,  since  the  diastoles  should 
aspirate  the  blood  in  the  two  cavse,  while  the  two  systoles  would  produce  high 
pressure  in  the  arterial  system  for  increasing  circulation  in  the  capillaries. 

'By  means  of  this  combined  action  in  the  placenta,  heart  and  vessels,  a  rapid 
circulation  is  readily  effected  under  the  high  pressure  that  obtains  in  intra- 
uterine  life  ;  but  anything  which  should  interfere  with  this  mechanics  by 
reducing  pressure,  e.g.,  escape  of  the  amniotic  fluid,  would  promptly  destroy 
life.  How,  otherwise,  account  for  this  circumstance,  since  the  vascular  connec- 
tions are  uninjured?  Moreover,  the  lividity  of  the  skin,  which  occurs  in  these 
cases,  proves  conclusively  the  existence  of  venous  stasis  in  the  systemic  capil- 
laries, and  insufficiency  of  the  heart's  action  to  carry  on  circulation  in  the 
absence  of  the  normal  pressure  upon  the  embryo.  The  same  circumstance 
occurs  to  the  air-breather  when  carried  to  too  great  an  altitude,  nothwithstand- 
ing  the  extensive  arrangements  for  changing  pressure  in  the  chest,  which  exist 
in  the  latter.  This  circumstance  may  be  especially  noticed  in  balloonists,  and 
also  in  persons  ascending  mountain  ranges,  respiration  and  circulation 
becoming  more  and  more  embarrassed  as  the  journey  is  proceeded  with, 
and  venous  stasis  more  and  more  conspicuous,  till  the  limit  of  endurance 
is  reached  or  life  itself  is  terminated,  as  occurred  in  the  celebrated  case  at 
Paris,  in  which  the  voyage  was  made  by  two  balloonists,  one  losing  his  life,  the 
other  being  unconscious  when  the  balloon  descended. 

THE   ACTION   IN   MEDUSA   CONTRASTED   WITH   THE   ACTION   IN  THE   PLACENTA. 

The  action  in  medusce  feeding  in  the  juices  in  the  sea,  piimping  them  in  and 
out  of  the  internal  compartments  by  means  of  rhythmical  expansions  and  con- 
tractions for  changing  pressiire  upon  them,  may  be  taken  to  illustrate  the 
mechanical  action  in  the  placenta,  which  feeds  in  the  juices  of  the  womb, 
pumping  them  in  and  out  itself  from  the  maternal  sinuses.  Thus  the  peduncles 
(Fig.  2,  a,  a,  a)  answer  to  the  tufts  while  the  mantle  represents  the  body  of  the 
placenta.  But  to  make  the  analogy  complete,  a  tubing  should  project  from  the 
convex  surface  of  the  latter  to  represent  the  umbilical  vein  and  arteries,  and 
which,  for  obvious  reasons,  are  not  present.  The  analogy  is  more  striking, 
however,  than  would  appear  on  the  surface,  since  from  the  periphery  of  the 
stomach  a  system  of  radiating  canals  extends  to  the  edge  of  the  mantle,  dividing, 
subdividing  and  anastomosing  to  form  a  continuous  and  complicated  capillary 
plexus  around  the  free  margin  of  the  mantle,  inclusive  of  the  colored  lobes,  to 
form  the  respiratory  apparatus.  This  may  be  taken  to  represent  the  circulation 
on  the  distal  side  of  the  placenta,  and  though,  for  obvious  reasons,  the  force  is 
increased  in  the  embryo,  still  the  mechanical  principle  is  the  same  for  both  cir- 
calations. 


In  tin-  mantle,  as  \\vll  as  in  the  placenta,  nnstri|>t-d  miiM-l.  ^  are  present  for 
hflMMillg  tin-  .•iiiT.i.'v  nf  tin-  rhythmical  expansions  ami  c.  mil-actions.  But 
muscles  arc  nut  essential  in  this  action,  a  notable  example  nf  which  is 
bnythed  in  tin-  In-art  itsi-lf,  which  expands  ami  cniitracts  rt'gularlv  and  rhvth- 
micallv  liefon-  a  nniscl.-  or  m-r\.-  is  ili-\  -loped  in  tin-  protoplasmic  and  un- 
diH'en-ntiated  \vallsip.  -J'.l'.li,  also  in  capillaries  ami  in  earlv  animal  forms. 

It  is  interesting  to  note  tin-  fact  in  ttris  connection  i  which  has  already  been 
comim-nt^l  upon  in  tin-  higher  stages  of  ili-vdnpnicnt  i.  that  <-r,ri/  ///<»(•.•;/<«•«/  of 
the  animal,  l.v  rxtrinHni,'  nr  retract in.i;  tin-  mantle  ami  tin-  Imincln-il  ]K3dtlLcle8, 
must  ./'//  increase  circiilatimi  ami  n-spiration  in  roiTespnnilence.  It  could 

not  In-  ntherwi>e.  Niiim-r..n-  -tminita  in  tin-  rounded  extremities  of  the  peduncles 
(a,  a,  "i  atl'onl  fi-ci-  in^i-i-ss  mid  ogress  to  the   tlimls   in  the  central  canals  (b,c). 


Fin.  2.— MF.DI-SA  (Rhtinntoma  cuvieri).  A,  a,  a,  eight  peduncles;  6,  c,  internal  canals  leading 
up  to  the  stomach;  <l,  stomach;  e,  e.  <?,  e,  aurmountinj;  ovarial  sacs  (four);  /,  k.  lateral  respi- 
ratory canals;  h,  h,  respiratory  lobes  on  free  margin  of  mantle  (colored);  I,  I,  thin  membranous 
l>  trillions  separating  the  caviiy  of  stomach  from  the  ovarial  sacs;  i,  i,  external  opening  to 
ovarial  sacs;  m,  oesophageal  passage.  (After  Grant) 


The  capillary  loops  at  the  sides  of  the  peduncles  (/,  k),  which  function  as  ab- 
sorb-in; and  respiratory  vessels,  may  be  taken  as  the  simile  of  the  capillary 
hxips  in  the  tufts  of  the  placenta. 

This  brief  description  will  serve  to  explain  the  mechanical  principle  in  the 
placenta,  and  it  now  remains  to  be  seen  how  this  action  is  assisted  by  the  action 
takin  j  place  in  the  womb  itself ;  or  how  the  maternal  and  foatal  circulations  are 
made  to  connect  for  effecting  mutual  interchange,  the  former  supplying  the 
nutritive  and  force-producing  elements  for  the  growth  and  elaboration  of 
tissue,  the  latter  yielding  up  the  waste  products  to  be  borne  back  through  the 
maternal  channels  to  the  environment  from  which  everything  is  derived,  and 
into  w!iich,  in  due  time,  everything  is  returned  in  the  form  of  waste 
and  tin  il  dissolution. 


MODE   OF   CONNECTING   THE   MATEENAL   WITH   THE   FCETAL   CIRCULATION. 

The  circulation  of  maternal  blood  in  the  uterine  and  placental  sinuses  is  the 
same  in  principle  as  that  for  circulating  air  in  the  lungs,  namely,  by  rhyth- 
mical changes  in  pressure  in  the  sinuses,  which  is  produced  by  the  action  taking 
place  in  the  womb  itself ;  taking  the  placental  sinuses  to  represent  the  alveoli, 
and  the  uterine  the  tracheal  system,  the  blood  flowing  in  and  out  of  this  system 
of  canals  by^reflux  action  for  renewal,  just  as  the  pulinonic  air  flows  in  and  out 
of  the  tracheal  system  for  renewal,  only  that  in  the  former  the  fluid  passes  into 
the  venous  system  of  the  mother  and  is  returned  by  the  arterial,  both  terminat- 
ing by  capillary  openings  in  the  canals,  while  the  placental  souffle  answers  to 
the  respiratory  murmur. 

We  have  already  spoken  of  the  role  which  the  placenta  plays  in  this  respect, 
and  it  now  remains  to  take  up  the  very  important  one  which  the  uterus  itself 


FIG.  3. — LONGITUDINAL  SECTION  OF  A  LATELY  GRAVID  WOMB,  showing  the  canal  system. 
Taken  from  a  case  of  post  partem  bffimorihage  (partly  diagrammatic).  1,  peritonieum ;  2, 
uterine  canals  (sinuses);  3,  openings  to  canals  on  the  mucous  surface  corresponding  with 
openings  to  placental  sinuses;  g,  Fallopian  tube;  /,  ligament  toTtrtCTyr-r,  round  ligament. 

(fir-tv^^l 

performs  for  completing  this  deeply-interesting  mechanics,  which  it   would  be 
difficult  to  overestimate,  underlying,  as  it  does,  embryonic  life. 
First,  with  regard  to  the  uterine  sinuses,  we  may  mention  that  this   canal 


a  which  is  channeled  in  the  walls  of  the  gravid  \\,m\l)  does  not  consist  of 
veins  or  arteries  enlarged  for  the  purpose,  but,  on  the  contrary,  that  the  proper 
substances  of  the  womb  itself  (muscles  and  connect  he  tissue  i  compose  the  actual 
walls,  which  are  lined  by  a  tleliente  uieinbnine  answering  to  the  lining  mem- 
brane of  the  vessels.  The  difference  is  very  material,  since  the  vessels  are 
enabled  to  expand  ami  contract  themselves  for  increasing  circulation,  while  in 
the  ca>''  of  the  sinuses,  the  walls  of  the  womb  would  have  to  expand  and  contract 
in  order  to  HIKW«-  circulation  in  them,  mid  that  this  is  the  case  will  appear  more 
obvious  as  we  proceed,  the  mechanics  undoubtedly  calling  for  such  a  condition. 

When  a  longitudinal  section  is  made  of  a  gravid  womb  at  full  term,  this  canal 
^v-teni  is  seen  to  traverse  its  substance  in  various  directions  from  near  the  central 
IM  nt  ions,  but  trending  to  the  internal  or  mucous  surface  where  they  connect  with 
the  placenta  (Fig.  3 — '2,  3).  They  never  penetrate  to  the  external  surface  to 
form  continuous  tubes  with  the  arteries  or  veins;  but  on  the  contrary,  both 
these  systems  of  vessels  connect  with  this  system  of  canals  by  means  of  capil- 
Itirit  ••*,  the  arterial  emptying  and  the  venous  discharging  from  these  common 
mains.  Hence  this  blood  is  mixed  as  a  matter  of  necessity. 

The  next  important  point  is  the  method  this  system  of  canals  exhibits  in  con- 
necting with  the  placenta!  sinuses,  which  is  done  by  projecting  the  lining  mem- 
brane in/')  l/i''  t>>(lixtan<-e  of  the  placenta  (Fig.  4,  c,  c,  c,  c).  This  spreads  out  at  once 


FIG.  4. — VKIUII  u.  SI:CTHI\  OK  I'I.ACF.NTA,  showing  arrangement  of  maternal    ami    f<rtul  vessels. 
A,  n,  chorion;  l>,  >>,  ileciilua;  0,  < .  .  .  . ,  urillres  of  uterine  sinuse.j.     (After  Dalton.) 

to  form  the  large  cavitary  spaces  in  which  the  highly   ramified  placental  tufta 
are  suspended  and  submerged  in  blood. 

The  walls  of  these  large  cavities  in  which  the  lining  membrane  of 
the  uterine  sinu>es  is  merged  answers  to  the  outer  surface  of  these  highly-rami- 
fied tufts  which  tit  into  this  as  the  fingers  in  a  glove,  the  vascular  loops  being 
contained  inside  of  them  (Fig.  5,  a,  a).  It  is  easy  to  perceive  that  this  out- 
side wall  and  the  wall  of  the  capillary  itself  in//  rr<  n<-  lx>tween  the.  maternal  and 
foetal  blood,  and  that  interchange  would  have  to  be  effected  through  these  two. 


8 

membranes ;  hence,  to  be  very  active  it  would  call  for  considerable  force  for 
producing  this. 


FIG.  5.— EXTREMITY    OF    FCETAL    TUFT,  from  human  placenta  at  term,  in  its  recent  condition. 
A,  a,  capillary  bloodvessels.     Magnified  135  diameters.     (After  Dalton.) 

During  attachment,  when  the  sinuses  are  filled  with  the  maternal  blood  they 
are  greatly  larger  than  after  detachment,  when  the  blood  is  forced  out,  and  the 
tufts  are  compressed  against  each  other  in  the  maternal  passages,  reducing 
the  placenta  fully  one-half  its  size.  At  the  time  of  birth,  the  necks  of  the 
uterine  sinuses,  where  they  join  the  placenta,  are  readily  torn  through  (Fig.  4, 
o,  c,  c,  c),  and,  peeling  off  easily  with  the  decidua,  the  organ  is  expelled,  unless, 
forsooth,  abnormal  nutritive  changes  in  the  parts  have  made  the  union  more 
intimate. 

The  problem  in  the  mechanics  concerns  the  manner  by  which  the  blood  is 
speeded  in  and  out  thesf  sinuses  commensurate  with  the  increasing  wants  of  the 
growing  embryo,  and  how  this  in  turn  is  connected  with  the  arterial  and  venous 
systems  of  the  mother  for  compelling  correspondence  in  them,  the  whole  forming 
&  connected  movement — a  movement  within  a  movement,  so  to  speak. 

We  have  seen  that  change  of  pressure  is  the  law  of  the  animal  circulation.,  ;md 
it  now  remains  to  make  rigid  application  of  this  principle  in  mechanics  to 
the  special  phenomena,  .anatomical  and  physiological,  appertaining  to  this  inter- 
esting region,  in  order  to  make  them  also  intelligible,  which  otherwise  are  utterly 
inexplicable. 

It  follows,  that  for  increasing  circulation  in  the  placenta  we  must  provide 
for  rhythmical  changes  in  pressure,  since  no  other  force  applies  for  producing 
it,  and  we  must  connect  the  action  in  the  womb  (which  expands  and  contracts 
regularly  and  rhythmically)  with  the  action  in  the  placenta,  so  that  when  the 
latter  [expands  for  producing  low  pressure,  the  former  contracts  for  producing 
the  opposite,  and  vice  versa. 

In  this  manner  an  active  circulation  in  and  out  the  placental  sinuses  could  be 
readily  produced. 

The  following  facts  may  be  given  in  support  of  this  opinion : 

1.  The  womb  must  expand  and  contract  regularly  and  rythmically  in  order  to 


increase  circulation  in  tin'  sinuses.  since  tliis  is  essential  for  changing  piw-.ure 
upon  tin-  l)l<HHl,  while  the  va^t  numlier  of  muscles  and  nerves  in  tln>  walls  of  the 
womb  are  the  provision  for  more  energetic  action  than  is  possible  to  the 
placenta,  which  is  composed  almost  entirely  of  vascular  loops. 

'2.  The  womli  .-.ii  IT*  HI  in/* -the  emliryo.  and  its  a<-tion  would  therefore  be  more 
etl'ective  for  producing  the  changes  in  pressure  upon  it,  which  is  also  in  imilnlii •/. 
<•('  ir/nit  t'iki'x  /ilni-i  in  /In- uiitiiinn  of  the  grow  ing  chick,  it  beJBgZOOked  to  mid 
fro  in  the  egg  b\  the  slow  rhythmical  expansions  and  contractions  taking  place 
iu  the  amnion  i|i.  -I'.I'.M.  and  by  alternating  this  ai-tion  with  the  one  taking  place 
in  the  placenta,  it  is  readilv  jH'rceived  how  a  rapid  circulation  could  be  main 
tained  in  the  maternal  and  placental  sinuses  for  compelling  correspondence 
lietwecn  this  and  the  energetic  circulation  in  the  emliryo,  since  it  all  forms  a 
connected  whole.  This  would  also  be  in  conformity  with  the  principle 
in  the  circulation,  the  blood  flowing  from  high  to  low  pressure.  As 
the  placenta  i-.i-fiiimlx  for  reducing  pressure  within  itself,  and  for  increasing 
pressure  in  the  emlir\o.  *///, <///«///.  ..W//  and  /»iri  JMWXH  with  this  action  the  entire 
muscular  walls  of  the  womb  <;<ntr<i<t  for  increasing  pressure  in  the  maternal 
sinuses  for  eomi>elliiig  this  blood  in  the  placenta,  at  the  same  time  by  increasing 
pressure  upon  the  embryo  it  should  determine  a  more  rapid  movement 
from  the  latter  to  the  placenta ;  the  one  involving  the  other.  But  when  the 
placenta  contracts  for  increasing  pressure  (thereby  compelling  the  blood  out 
of  itself  in  two  directions,  or  toward  the  embryo  and  the  maternal  sinuses), 
the  uterine  walls  expand  for  reducing  pressure  in  the  embryo  and  the  uterine 
Minist  s,  thus  greatly  expediting  the  placental  efflux;  and,  taking  it  all  in  all, 
there  can  lie  very  little  doubt  but  that  the  force  which  is  represented  in  the 
muHled  murmur  of  the  placental  souffle  is  mainly  the  product  of  the  muscular 
uterine  walls,  though  l>oth  undoubtedly  contribute  to  it. 

'.'<.  This  action  in  the  uterus  and  placenta  would  account  for  the  very  curious 
and  suggestive  n/i/ii/n////  in  that  portion  of  the  canals  connecting  the  uterine 
with  the  placental  sinuses,  being  upon  a  line  almost  paraUeJ  with  the  transverse 
axis  of  the  uterus  and  placenta,  which  is  precisely  what  is  called  for  by  the 
special  mechanics,  in  order  to  effect  the  lateral  or  to-ond-fro  movements,  the 
vessels  simply  elongating  and  contracting  with  these,  as  the  case  may  be,  with- 
out interfering  with  the  calibre  of  the  tubes.  Were  the  vessels  straight,  it 
would  be  utterly  impossible  to  operate  this  mechanics,  since  the  lateral  move- 
ments should  obliterate  the  vessels  by  closing  the  calibre.  It  could  not  be 
otherwise,  in  the  very  nature  of  things.  In  the  accompanying  diagrams  (Figs. 
3,  4),  the  vessels  are  represented  as  nearly  perpendicular,  but  this  is  done 
simply  for  better  definition. 

I.  lint  the  strongest  proof,  perhaps,  of  this  higher  function  of  the  womb  is 
furnished  in  the  \asmlar  and  nervous  connections  subsisting  lietween  it  and 
the  maternal  organism.  And  as  all  this  relates  to  circulation  for  building  up 
and  elaborating  the  embryo,  obviously  the  mechanics  for  increasing  circulation 
in  the  womb  commensurate  with  that  in  the  embryo  should  extend  to  the  vessels 
of  supply  or  the  feeders,  as  also  the  discharging  vessels,  or  the  arteries  and 
\eins.  It  must  be  shown  how  this  new  movement,  this  new  life  set  going 


10 

within  the  other,  twines  its  arms  around  the  maternal  vessels  and  feeds  itself  in 
the  measure  of  its  necessities,  by  means  of  this  pumping  action  in  the  womb  and 
placenta  which  represents  respiration.  The  spermatic  and  uterine  arteries  are 
the  feeders  (Fig.  6,  <s,  «),  while  the  accompanying  veins  are  the  discharging 


FIG.  6.— Showing  the  ARTERIES  AND  VEINS  TO  THE  WOMB,  fi,  spermulic  artery  and  veins 
(ovarian);  u,  uterine  artery  and  vein;  1,  vessels  passing  between  the  muscular  fibres:  2,  peri- 
toneum; g,  Fallopian  tube;/,  ligament  of  ovary;  r,  round  ligament:  /',  inferior  ligament  or 
duplicating  of  peritonaeum  corresponding  with  Douglas's  Cttl  de  eac;  r.  vagina. 

vessels.  To  this  must  be  added  the  uterine  lymphatics,  which  arc  very  large  in 
the  impregnated  womb.  They  terminate  in  the  pelvic  and  lumbar  glands.  The 
spermatic  arteries  and  veins  have  similar  origin  and  termination,  as  in  the 
male,  while  the  uterine  artery  is  a  branch  of  the  internal  iliac,  with  the  venous 
return  through  a  vein  of  the  same  name.  The  deeply  suggestive  fact  to 
note  in  this  connection  is  that  the  dense  plexuses  of  nerves  to  the  fundus  and 
sides  of  the  womb  converge  in  the  nervous  ganglia  about  these  vascular  trunks, 
or  the  spermatic  and  hypogastric  ganglia  (Fig.  7,  e,  ir,  r).  It  will  be  seen  that 
the  nerves  to  the  fundus  (v,  x)  converge  in,  or  radiate  from,  the  spermatic  gan- 
glion (ic),  which  surrounds  the  spermatic  artery  and  vein  (e)  (which  corresponds 
with  the  attachment  of  the  placenta),  while  those  in  the  neck  and  sides  from  the 
hypogastric  ganglion  (r)  are  brought  in  direct  relation  with  this  ganglion  by 
means  ot  intercommunicating  nerves  (/)  for  unifying  the  action  throughout. 
Tims,  nervous  force  to  the  womb  is  literally  lanked  upon  the  bloodvessels, 


3 


KliJ.    7     <;\\..i.i\      \\n    NI.KW.S    in      inn    liiimn    lm:i  s  AT  THfc   Kxt>  OK    TI1K    NINTH    MONTH. 
.1.  tin'  fnndus  and  bod)  o(  Ilu-  uterus,  having  Hie  peritonaeum  diss<cted  off  from  left  side;   b, 
the  vagina  covered  willi    nerves  proceeding   Irom  the   inferior  bonier  of  the  left   livpoi::i.-liii 
ganglion:  e,  rectum:  </.  left   ovarimn  ami  Kallopian  tube;  e,  trunk  of  left  spermatic  vein  and 
artery  eurroanded  by  tin-  left  spermatic  ganglion;  /,  aorta  divided  above  the  oripin  of  the 
right  speimatic  artery:  ;/,  venacava:  h,  trunk  of  right  spermatic  vein:  i,  ri^'lit  ureter:  k.  Hie 
I  HO  copl-  'if  the  ^reat  .-ivinputhetii-  pussin^  down  along  the  front  of  aorta:  /.  trunk  of  inferior 
•I'titenc  artery  with  the  nervous  plexus  connecting  with  the  right  and  left  cords  of  Hie 
ijiallietk-;   //,.  1 1n' two  cords  of  the  i;reat  sympathetic  at  '.he  lioint  of  bifurciition  into  tin- 
riu'lit  and  left  hypo^aslric  nerves;   n.  r\f\\\  hypoi;:iftric  nerve  with  its  artery  injected,  procetd- 
ini;  to  neck  of  uterue  to  terminate  in  the  ri^'lit  h\pn<;astnr  gati.nlion;  <>,  left  bypoaMlta  nerve 
B  left    hjpou'astric   ^iingliii,  and  ^ivin^  oil   branch'-  to  the  left  gub-peritoneul 
^an^lia  :  ,i.  hxmorrfaolda]  nerves  and  arterj  :  •/.  sacral  nerves  entering  the  whole  outer  surface 
of  the  hjpoga-trir  gunglion:  r,  left   hypogiistric  ganglion  with  the  arteries  injected;  »•.  nervi- 
of  i  '.  nerves  with  an  injected   arlen  proceinling  from  the  upper  part   of  left  hypn- 

L':i-tric  ganglion  along  the  body  of  the  uterus,  and  terminating  in  the  left  spermatic  ganglion: 
'i.  continuation  of  these  nerves  and  the  brunches   which    they   L'ive  off  In  the  snb-peritoneal 
plexuses:    /-.  >oine  nen es  passing  upward  beneath  the  sub-peritoneal  plexuses;  and  an 
nici.-ing  fiee|\  with  them;   "•.  left   :-pcriu:itic  irangliou.  in  which  the  nervea  and  artery  from  the 
hyiiog.istric  ganglion,  and  the  branches  of  the  lefi  sub  peritoneal  plexuses  terminate,  and  from 
which  the  nerves  of  the  fiindus  uteri  are  supplied:  .r,  left  sub-|ieriton«'al  plexuses  covering  the 
Ixxh  of  the  uteru>:   //.  left  sub-peritoneal  ganglion,  with   numerous  brandies  of  nerves  exten. I 
ing  between  it  and  left  li\  nerve  and  ^arglia:  ^,  left  common  iliac  artery  cut  across 

and  turned  aside  to  expose  left  hypogastric  nerve  and  ganglion.     (After  Dr.  R.  Lee.) 


12 

and  if  this  means  anything  it  means  that  circulation  shall  be  in  correspondence 
with  the  physiological  requirements,  or  supply  equal  to  demand,  the  cardinal 
circumstance  being  the  </i-»t/1/i  and  elaboration  <>f  the  embryo,  which  is  the  object 
and  purpose  of  the  organ,  the  others  being  simply  incidental. 

It  conies  to  this,  namely,  that  the  nervous  force  for  expanding  and  contracting 
the  uterine  sinuses  should  expand  and  contract  the  uterine  bloodvessels  at  one 
and  f/ie  n<une  time,  thereby  causing  afflux  and  efflux  of  blood  through  them  for 
compelling  correspondence  throughout  which  the  scheme  calls  for.  Furthermore, 
this  wou'd  accord  with  the  action  in  the  vessels  in  respiration,  as  indicated 
by  the  undulations  in  arterial  tension.  But  would  not  this  mechanics  inter- 
fere with  the  due  circulation  of  blood  in  the  placental  sinuses'?  Certainly 
not,  and  for  the  following  reasons :  1.  Efflux  of  blood  through  the  veins 
is  by  means  of  capillary  vessels,  which  tend  to  retard  escape,  while  the  flow  of 
blood  in  and  out  the  placenta]  sinuses  takes  place  through  large  canals  (Fig. 
5,  c,c,  c,  r).  But  in  addition  to  this,  the  expansion  in  the  placenta,  which  occurs 
during  systole  of  the  womb,  should  also  determine  the  blood  in  this  direction. 

2.  During  diastole  in  the  womb  and  its  sinuses,  for  aspirating  the  placental 
sinuses,  the  hic/h  j»-i'xsuri-  in  the  arterial  system  causes  this  blood  to  flow  into 
the  uterine  sinuses  as  rapidly  as  the  blood  coming  from  the  placenta ;  at  the 
same  time,  the  valves  in  the  veins  of  the  uterus  obviate  reflux  from  the  venous 
a- if  stem.  When  the  womb  contracts  for  compelling  the  blood  in  the  placenta 
and  venous  system,  the  pressure  in  the  arterial  inhibits  reflux  in  this  direction. 
Thus  the  mechanics  for  increasing  circulation  in  the  uterine  and  placental 
sinuses  is  complete  in  every  respect,  nor  does  it  require  extensive  expansion  and 
contraction  in  the  womb  in  order  to  effect  increased  circulation  through  the 
sinuses,  but  a  moderate  and  limited  amount,  sufficient  only  for  producing 
rhythmical  changes  in  pressure  upon  Hie  blood,  as  must  appear  obvious  :  some- 
thing similar  to  what  takes  place  in  the  spongiic,  which  have  muscles  (Norway) 
for  producing  a  more  rapid  circulation  in  and  out  this  canal  system. 

Tltis  expansion  of  the  irouJ)  and  arterial  feeders  would  explain  the  sudden  and 
enormous  escape  of  arterial  blood  in  post  partem  haemorrhage,  for  the  placenta 
being  no  longer  attached,  the  flow  of  blood  through  the  uterine  sinuses  must 
necessarily  be  purely  arterial.  In  other  words,  when  contraction  ceases  and 
the  movement  of  expansion  sets  in,  the  flood-gates  are  thrown  open  to  the 
arterial  system. 

In  reference  to  the  nervous  centre  for  this  pumping  action  in  the  womb, 
which  answers  to  respiration  in  the  foetus.  There  can  be  very  little  doubt 
but  that  the  spinal-cord  functions  as  the  common  reflex  centre  of  nervous  force 
for  producing  the  rhythmical  expansions  and  contractions  in  the  gravid  womb 
simulating  respiration.  The  following  are  the  reasons  for  this  allegation  :  1. 
The  very  intimate  connection  subsisting  between  the  womb  and  spinal  cord  by 
means  of  the  hypogastric  ganglia  and  sacral  plexus  with  the  intercommunicating 
nerves.  2.  The  fact  that  the  lumbar  portion  of  the  spinal  cord  undergoes  en- 
largement during  gestation  (Mathews  Duncan).  3.  The  fact  that  reflex  action  in 
the  womb  is  readily  produced  by  applications  to  the  skin  surface,  a  circumstance 
well  known  and  practised  by  the  profession.  All  these  facts  fall  readily 


i:: 

into  line  when  viewed  from  this  standpoint,  and.  no  scientific  reason  existing  in 
the  eontrarv.  we  may  conclude  tin-  fact  MS  logically  pio\en.  Indeed,  the  gist  of 
tin-  question  is  not  win-tin  i  'tin  TI  'is  a  retlex  centre  in  tlir  spinal  cc.nl  fur  the 

womb.  Imt  whether  this  centre  produces  tin-  rhythmical  expansion*  and  oontno- 

tions  in  that  organ  :is  alleged.  A  full  and  sulVicicnt  answer  to  this  is  fnmislicil 
.11  the  fact  nf  tlif  total  absorption  of  tin  relative  phenomena,  :matomic;il  and 
physiological,  w  hieh  otherw  U,-  are  utterly  inexjilicalile,  underneath  all  which 
:s  the  organic  law  on  which  animal  life  itself  is  constructed,  railing  for 
rhythmical  changes  in  pressure  in  the  contents  of  the  gravid  womli  and  in  the 
uterine  sinuses  for  increasing  circul at  ion.  Nor  is  it  reasonable  that  the  enor- 
nions  nunil>er  of  muscles  and  nerves  in  the  woml)  are  for  compelling  Otti  the 
cmiteiits  at  the  end  of  the  term  simply.  Imt,  on  the  contrary,  that  they  jH-rform 
an  active  and  essential  part  in  the  work  of  construction  whirh  ]>rci-edc8  expul- 
sion, lieyond  a  shadow  of  a  doiilit.  they  arc  not  idle  in  all  this  while. 
:ally  when  supreme  necessity  would  h:ive  it  otherwise;  Oil  the  contrary, 

they    an-  n*   /'<•/•'-  /•«/    for   carrying  on   circulation,   while  at 

the  end  of  the  term  they  are  available  for  insisting  in  expelling  the  embryo, 
hence  pe,  form  an  active  ;••./<  from  the  beginning  to  'the  end  of  their  existence, 
as  is  e\er  the  c;i.se  with  tin-  miiM-les  and  nerves. 

( )nc  oth'-r  circumstance  in  tliis  connection,  namely,  the  very  l<n-ln<»ui  course 
of  the  arteries  in  the  womb  i  Fig.  C>  i,  which  undoubtedly  is  adjustment  with 
this  action,  |K'rinittiiif;  the  rhythmical  ex]iansions  and  contractions  to  take  place 
without  involving  any  strain  to  the  vessels.  The  veins,  it  will  be  perceived,  taki > 
a  straight  (Miu-sc,  wliile  the  arteries  are  serpentine  or  ln>nt  njvm  themselves. 
HUB  is  tine  to  the  fact  that  the  veins  are  more  extensile,  and  possess  greater 
IMI-.VCI-S  of  elon^atiiiL,'  and  shortening  than  the  arteries,  the  yellow  elastic  coat  of 
the  latter  tending  to  limit  their  actions.  It  will  IK?  remembered  that  this  cir- 
ciini.-t  nice  has  forcible  illustration  in  th"  splenic  artery  and  vein,  the  former 
being  almost  twice-  the  length  of  the  latter,  to  allow  for  expansion  in  the  stomach 
when  fixxl  is  taken,  otherwise  this  would  involve  prodigious  strain  to  the  vessels, 
with  great  re  luction  of  the  calibre.  But  the  same  remark  will  apply  to  the  ves- 
sels of  all  the  hollow  viscera.  Thus  everything  is  in  correspondence.  Of  course, 
the  arc  of  movement  in  the  womb  and  placenta  is  necessarily  more  limited  than 
in  the  lungs,  in 'which  considerable  space  is  required  for  sucking  in  the  air 
simultaneously  with  the  venous  blood,  but  which  would  not  apply  for  the  foetal 
circulation,  as  the  oxygen  is  furnished  by  art.-ri.'il  blood  at  "/»•  «ml  the  samr  lini' 
with  the  nutritive  and  force-producing  elenvnts,  which  the  scheme  calls  for  in 
order  to  generate  force,  since  it  is  by  a  combination  of  the  two  that  force  is 
evolved.  The  inclusion  of  the  intestines  with  respiration  by  means  of  the 
I meumogostric  nerves  has  its  explanation  in  this  circumstance,  as  has  been 
fully  set  forth  in  the  preceding  pages.  Differentiation  in  the  organs 
cannot,  for  obvious  reasons,  work  any  change  in  the  fundamental  principle 
underlying  the  mechanics  for  increasing  circulation,  which  is  by  rhythmical 
changes  in  pressure  involving  a  pumping  action  for  compelling  the  commerce  in 
the  bloodvessels  and  expelling  waste  products,  while  the  speed  of  the  currents 
thus  produced  is  determined  by  the  rapidity  and  energy  of  the  rhythmical  ex- 


14 

pausions  and  contractions  pervading  the  organs,  inclusive  of  the  heart  ami 
vessels,  since  it  all  forms  a  connected  movement  for  increasing  circulation  be- 
tween the  cell  brood  and  environment,  from  which  everything  is  obtained  and 
into  which  the  waste  products  are  returned,  the  two  going  on  simultaneously. 

With  the  expiration  of  the  intra-uterine  term,  expansion  of  the  maternal 
passages  sets  in  for  reducing  resistance  to  the  egress  of  the  embryo, 
and  the  womb  and  abdomen  contracting  simultaneously  for  increasing  pressure 
in  the  womb,  the  contents  are  compelled  out  in  the  environment.  Here,  as 
elsewhere,  the  Jaw  of  pressure  applies  for  compelling  n/nri'/ncnf  in  flic  con- 
tents of  the,  Iwlloiv  viscera  for  which  xj>fri<t/  adjustments  obtain  in  the  organs  and 
organism,  the  underlying  principle  being  rhythmical  i-lnn/ifs  hi  jircsNim: 

The  atmosphere  being  invisible,  it  is  difficult  to  realize  the  important  relations 
this  sustains  to  the  mechanics,  nevertheless,  the  fact  is  incontrovertible,  that 
from  centre  to  circumference,  and  from  surface  to  surface  of  the  body  it  is 
corner-stone  and  foundation  to  all  t/te  mechanics  conccnii-i/  in  circulation. 

It  is  passing  strange  the  matter  should  have  escaped  attention  so  long, 
espacially  in  this  age,  when  thnujh.f  is  reaching  do.vn  into  the  organic  basis  of 
life.  Indeed,  one  needs  to  go  there  if  he  would  unravel  the  tangled  skein 
in  animal  structure  and  function,  since  the  definite  arrangements  that  obtain  in 
the  organs  with  every  stage  in  development  show  unmistakably  a  common 
relation  to  fundamental  forces  in  nature  underlying  it  all,  notably  pressure  run/ 
gravitation.  The  animal  body  is  not  outside  and  independent  of  the  organic  laws, 
but,  on  the  contrary,  is  in  entire  conformity  with  them,  while  the  arrangements 
which  obtain  in  the  structures  represent  the  relative  adjustments  for  special 
work. 

KESPIEATION    IN  THE  NEW-BORN  :    THE   CHANGE    IN    MECHANICS    WHICH    THIS  INVOLVES. 

The  first  thing  in  the  new-born  is  to  start  respiration  for  compelling 
in  the  commerce  in  the  environment  in  place  of  the  uterine  sinuses,  and 
the  action  in  the  placenta  for  which  this  is  the  substitute,  the  oxygen  passing 
in  by  way  of  the  kings  and  the  aliment  through  the  intestinal  canals.  But  this 
requires  fresh  adjustments  in  the  mechanics  of  circulation  to  bring  it  in  cor- 
respondence with  this  circumstance,  notably,  circulation  of  the  blood  in  the 
lungs,  and  the  attaching  of  the  intestinal  apparatus  to  this  movement  by 
means  of  the  nerves  connecting  in  the  medulla  oblongata,  a  matter  which  has 
already  been  fully  considered  in  the  preceding  pages.  The  first  thing,  there- 
fore, is  to  start  respiration,  when  it  will  bo  in  order  to  consider  how  tin 
mechanics  in  circulation  swings  into  this  pendulum  movement  for  compelling 
correspondence  throughout,  with  the  blood  ever  flowing  from  high  to  low 
pressure  in  conformity  with  the  organic  law  underlying  the  organism  itself. 
One  end  of  the  nervous  system,  so  to  speak,  is  .t/iread  out  in  the  skin 
surface,  the  other  through  the  organism,  while  the  medulla  oblongata  functions 
as  the  common  centre  to  it  all ;  any  impression,  therefore,  made  upon  the  skin 
surface  is  promptly  reflected  to  the  medulla  oblongata,  thence  over  all  the 
structures  for  producing  the  reflex  actions  connected  with  respiration  and 
circulation,  The  irritations  attendant  upon  parturition  from  friction  agains*- 


15 

tlir  maternal  structure^  .-in-  calculated  to  produce  these  reflex  actions; 
l>ut  tlir  contact  nf  tin-  sentient  surface  \vitl>  the  stiiiuilus  in  tho  atmosphere  itself 
woiiM  also  excite  it.  And  if  tin-  child  should  lie  injured  by  tin'  rude  experii-ne.-s 
incident  il  to  |>.-irtiiritii>n.  a  yet  more  powerful  means  fur  exciting  tin-  reflex 
actions  connected  with  respiration  is  furnished  by  the  su.ldeii  application  of 
cold  t  i  the  surface,  as  in  sprinkling  cold  water  upon  it,  or  a  sudden,  shurp 
slap  with  the  open  hand  may  lie  substituted  instead,  as  is  commonly  practised. 
List,  lnit  not  least,  c.irlionie  arid,  ;LS  it  accumulates  in  .the  blood,  acts  UK 
a  special  stimulus  to  respiration.  It  cries  out  hi  pain,  and,  presto!  the 
liemal  mechanics  is  changed.  The  low  pressure  which  is  produced  in  the 
aheoli  by  expansion  of  the  lung's  during  inspiration  compels  xiiiinllnin-onn  afflux 
of  air  and  blood  in  the  alveoli  ;  while  the  high  pressure  which  is  produced  l>v 
tin-  subsequent  c-int  ruction  during  e\]iinition  causes  *////«//</»<.,»>  efflux  in 
these  tluids.  which  (low  from  high  to  low  pressure  in  conformity  with  organic 
law  the  one  (lowing  out  liy  retlux  action  through  the  route  of  ingress,  the 
oilier  p.-is.,iiu  into  'he  left  chambers  of  the  heart  and  arterial  system  on  its  way 
to  the  cell-liroo  1.  as  has  already  been  described  in  the  air-breather.  This 
•I'.aiidonment  of  the  old  route  for  the  new  is  readily  explained,  since  it  is  in 
sti  ict  accordance  with  physical  law,  l>eing  in  the  direction  of  least  resistance. 

For  example,  we  /<•<//«  the  mechanics  with  high  pressure  in  the  arterial  sys- 
since  this  extends  through  tho  ductus  arteriosus  to  the  semilunar  valves  of 
the  pulmonary  artery,  the  floor  of  support  to  the  arterial  column.  Hence,  when 
the  alveoli  expand  during  inspiration  for  sucking  in  air  through  the  trachea, 
the  high  pressure-  in  the  pulmonary  artery  and  ductus  arteriosus  compels  this 
blood  to  flow  straight  on  to  the  low-pressure  areas  in  the  alveoli  rimulianeaualy 
\\ith  the  alflux  of  air,  or  in  the  direction  of  least  resistance,  in  place  of  forcing 
its  way  in  the  arterial  system  against  high  pressure,  which  would  be  contrary  to 
law.  And  the  ductus  arteriosus,  though  still  filled  with  blood,  as  in  the  case  of 
an  artery,  beyond  the  ligature  to  where  a  collateral  branch  is  given  off,  shrinks 
an  1  contracts  till  it  becomes  a  solid,  impervious  cord. 

For  closing  the  foramen  ovale  the  following  mechanics  apply:  After  birth 
the  inpour  of  blood  in  the  left  auricle  by  way  of  the  pulmonary  veins  is  as 
rapid  as  it  is  in  the  right  auricle  through  the  venae  cavse,  and  pressure  is  at 
equilibrium  in  the  two  auricles,  which  at  once  suspends  all  tendency  in  the 
lil  ood  to  pass  from  one  side  into  the  other  during  auricular  diastole  ;  whilst 
during  the  auricular  systole  and  the  high  pressure  this  produces  hi  the  auricles 
causes  this  blood  to  flow  into  the  expanding  ventricles,  where  low  pressure 
invites  it,  the  same  applying  for  either  auricle.  But  gravitation  also 
should  compel  it  in  this  direction,  since  the  ventricles  are  under  the  auricles. 
Thus  a  dual  force  applies  (suction  and  gravitation)  for  compelling  this  blood  in 
the  ventricles  during  the  auricular  systole,  and  the  foramen  ovalu,  being  thus 
abandoned,  is  closed  and  obliterated  by  membranous  formation. 

But  in  uitra-uterine  life  the  matter  is  different  ;    here   the    whole  blood    is 


•  The  intimate  connection  galisiuinu'  iwtw.f  i  in.-  r  ••>:>!  r.  ,ui'l  the  glcin  an  Tun-  ia  of 

•  •.!->   'li'inninlratiiMi  in   tin1  tulult   liy   tin1  sann-  IIH-  i;is.     Kur  fxample,  every  impact  of  mid  walrr 
•   tin*  akin  i>r."'l  !.••'•-  <|i  i~  n<>  lir  iuspinilinu  or  ex[>  union  ill  tlie  luiigi  ;  not  deep,  however, 
l>ul  very  energeiir. 


1(5 

poured  into  the  right  auricle,  that  from  the  upper  cava  passing  at  once  in  the 
right  ventricle,  while  that  in  the  lower  cava  (which  includes  the  blood  from  the 
umbilical  vein)  passes  through  the  right  into  the  left  auricle,  with  which  it 
directly  communicates,  guided  by  the  Eustachian  valve,  but  also  pushed  over 
and  deflected  in  this  direction  by  the  weight  of  the  descending  current  from 
the  upper  cava  ;  but  if  the  head  be  downward  then  by  its  own  weight  the  blood 
would  gravitate  in  this  direction,  the  influx  of  blood  from  the  upper  cava  also 
compelling  it.  And  'with  the  absence  of  blood  as  a  counter-force  in  the  left 
auricle  this  blood  is  necessarily  compelled  in  the  latter,  thence  in  the  left  ven- 
tricle and  aorta,  while  that  in  the  right  ventricle  passes  in  the  arterial  system 
at  the  aortic  arch  by  way  of  the  pulmonary  artery  and  ductus  arteriosus.  After 
birth,  however,  the  pumping  action  in  the  lungs  reverses  all  this  in  manner  as 
above  described.  The  pulmonary  artery  in  the  embryo,  in  place  of  dis- 
charging through  the  lungs,  left  auricle  and  ventricle,  empties  its  blood  at 
once  into  the  aorta  as  it  passes  under  the  arch,  and  which  is  also  in  the  direction 
of  least  resistance,  since  it  is  impossible  for  this  blood  to  thread  its  way 
through  the  capillary  meshes  of  the  unexpanded  alveoli.  This  circumstance  has 
forcible  illustration,  even  in  the  air-breather,  and  when  the  alveoli  are  filled 
with  residual  air,  by  simply  inhibiting  inspiration  by  closing  the  mouth  and 
nose  so  as  to  prevent  expansion  in  the  lungs,  the  blood,  in  consequence,  rapidly 
accumulating  in  the  right  side  of  the  heart  and  venous  system.  Tn  the  space 
of  a  minute  there  is  lividity  of  the  lips  and  whole  cutaneous  surface  from 
venous  stasis  in  the  systemic  capillaries.  If  longer  than  this,  an  appalling 
venous  suffusion  pervades  the  surface ;  in  the  face  most,  for  this  is  the  most  vas- 
cular portion,  with  the  large  venous  trunks  in  close  proximity  to  the  heart. 
Even  the  eyes  are  forced  outward,  becoming  prominent  from  distension  of  the 
iutra-orbital  veins  caused  by  obstruction  in  the  cavernous  and  lateral  sinuses. 
But  the  instant  the  obstruction  is  removed  and  the  lungs  are  permitted  to 
expand  the  dammed-up  blood  surges  through  the  alveoli,  and  all  runs  on  as  be- 
fore. In  other  words,  the  heart  and  vessels  are  unable  to  carry  on  circulation 
in  the  absence  of  the  pumping  action  in  the  lungs,  for  which  afflux  and  efflux 
of  air  is  essential.  But  all  this  has  been  sufficiently  explained. 


INCUBATION.      CIRCULATION   IN   THE   EGG. 

Why  should  there  be  an  air-chamber  to  the  egg  (Figs.  8  and  9)  ?  We 
are  now  prepared  to  furnish  a  scientific  explanation  to  this  physiological  problem, 
otherwise  inexplicable,  viz.,  the  contents  of  the  egg  for  developing  the  chick  is 
enclosed  by  a  firm  unyielding  wall  of  living  marble,  and  since  the  animal  circu- 
lation is  dependent  upon  rapid  rhythmical  changes  in  pressure,  it  follows  that 
provision  should  be  made  within  the  shell  for  effecting  this,  otherwise  the  action 
in  the  heart  and  vessels  could  not  take  place.  This  air-chamber  (g),  together 
with  the  important  relations  it  sustains  to  circulation  and  elaboration  in  the 
growing  chick,  organilogically,  therefore,  must  be  regarded  as  one  of  the  most 
essential  and  important  elements  in  egg-structure,  the  underlying  principle  to  all 
the  nutritive  changes  which  are  ushered  in  under  the  action  of  external  temper- 


17 

iituri'.      The    Hccomiunvin^    illustration    i  FiU'.   Hi    will   serve  to    impress    the 
mutter. 

Tin-  discipline  in  tin-  nutrithe  processes  requin-s  the  blood  to  be  brought 
from  tlie  vitellus  and  a  •  rated  in  the  allantois.  thence  to  be  dispatched  through 
the  Imdy  territories.  Accordingly  tun  great  venous  trunks  (omplialo-meseraic 
veins i,  one  in  each  fold  of  the  aplanahnopfetm,  embnofng  the  vitellus,  are  the 


KI<;.  s.  MuiiRAM  OK  l-ntti.'-  Koa.  A,  yelk;  '.  vitel!im>  membrane;  c,  chnlaziferous  membrane; 
d,  albumen;  e.  f.  miililli*  anil  internal  shell  memiirane.-i :  y,  uir  chamber;  A,  calcareous  shell. 
(Aft«r  Dalton.) 

first  evolved,  while  at  the  terminal  ends  or  confluence  the  heart  is  formed  by  the 
blending  of  the  walls  of  these  venous  trunks. 

According  to  His.  the  heart  is  developed  by  the  coalescence  of  a  layer  of  the 
splauchnopleure  with  a  similar  layer  from  the  somatopleure,  the  hollow  cavity 
formed  by  the  union  bein^  in  free  communication  with  the  adjacent  omphalo- 


FIC.  !).  —  Eoo    or    FOWL  is   I 'HOC  BSD 
circulation,  terminal  sinus,  etc. 


[)KVKt.opjiEXT,  showing  area  vasculo.ia.  with  vitelllne 


meseraic  veins.  According  to  Foster  and  Balfour  "  the  upper  end  of  the  heart 
is  developed  out  of  the  mesoblast  of  the  splanchnopieure,"  but  "  increases  in 
length  step  by  step  at  the  expense  of  the  continually  coalescing  ouiphalo- 


18 

meseraic  veins."  Thus  the  fact  is  undeniable,  that  the  heart  is  developed 
in  the  venous  system  in  connection  with  the  vitettus.  The  rhythmical  ex- 
pansions and  contractions  in  this  organ  (the  punctum  saliens  of  early  authors) 
serve  to  pump  the  vitelline  fluids  in  the  bulbus  arteriosus  and  the  two  aortse 
which  are  developing  at  the  other  end  of  the  heart.  But  for  this  air-ciishion 
within  the  egg  (Figs.  8  and  9,  g),  neither  these  rhythmical  expansions  in 
the  heart  nor  the  changes  in  pressure  for  compelling  circulation  in  the  vitelline 
fluids  could  take  place,  since  the  unyielding  shell  would  inhibit  these  actions,  as 
must  appear  obvious. 

Respiration  is  provided  for  in  the  following  manner :  The  aUantois  (a  diverticu- 
lum  of  the  intestinal  canal)  is  pushed  out  around  the  amnion  which  contains  the 
embryo,  and  expanding  its  vast  capillary  net-work  of  vessels  (whose  footstalks 
spring  from  the  two  iliac  arteries,  as  do  the  umbilical  arteries  in  the  mammalian 
embryo)  against  the  shell-membrane  or  chorion  becomes  the  respiratory  organ  of 
the  chick,  by  means  of  which  the  venous  blood  is  constantly  arterialized,  the  oxygen 
passing  in  and  the  carbonic  acid  passing  out  through  the  pores  in  the  shell  by 
the  action  of  the  polar  forces.  But  "  at  the  time  the  heart  first  begins  to  beat, 
the  capillary  system  of  the  vascular  and  pellucid  areas  is  not  yet  completed, 
and  the  fluid  which  is  at  first  driven  by  the  heart  contains,  according  to  most 

observers,  very  few  corpuscles The  course  of  the  blood  then, 

during  the  latter  half  of  the  second  day,  may  be  described  as  follows :  The 
blood  brought  by  the  omphalo-meseraic  veins  falls  into  the  twisted  cavity  of 
the  heart,  and  is  driven  thence  through  the  bulbus  arteriosus  and  aortic 
arches  into  the  aortic  trunk.  From  the  aorta  by  far  the  greater  part  of  the 
blood  flows  into  the  omphalo-meseraic  arteries,  only  a  small  amount  passing  on 
into  the  caudal  terminations.  From  the  capillary  net-work  of  the  vascular  and 
pellucid  area  into  which  the  omphalo-meseraic  arteries  discharge  their  contents, 
part  of  the  blood  is  gathered  tip  at  once  into  the  lateral  or  direct  trunks  of  the 
omphalo-meseraic  veins.  Part,  however,  goes  into  the  middle  region  of  each 
lateral  half  of  the  sinus  terminalis,  and  there  divides  on  each  side  into  two 
streams.  One  stream,  and  that  the  larger  one,  flows  in  a  forward  direc- 
tion until  it  reaches  the  point  opposite  the  head,  thence  it  returns  by  the 
veins  spoken  of  above,  straight  to  the  omphalo-meseraic  trunks.  The  other 
stream  flows  backward,  and  becomes  lost  at  the  point  opposite  the  tail."* 

The  following  from  the  same  authors  is  deeply  suggestive:  "Soon  after  its 
formation  the  heart  begins  to  beat,  at  first  slow  and  rare  pulsations,  beginning 
at  the  venous  and  passing  on  to  the  arterial  end.  It  is  of  some  interest  to  note 
that  its  functional  activity  commences  long  before  the  cells  of  which  it  is  com- 
posed shoiv  any  distinct  differentiation  into  muscular  or  nervous  elements."  It 
would  be  difficult  to  overestimate  this  circumstance,  since  it  establishes  beyond 
peradventure  the  power  in  the  higher  as  in  lower  animals  to  effect  rhythmical 
expansions  and  contractions  in  the  soft  tissues  in  the  absence  of  any  muscle  or 
nerve  for  producing  them.  But  at  present  the  significance  of  these  rhythmical 
expansions  and  contractions  taking  place  in  the  heart  concerns  us  most,  since 
the  manifest  purpose  is  to  increase  circulation  ;  and  as  this  can  only  be  done  by 

*  Fos'.er  and  Balfour's  •'  Embryology." 


1'.' 

pumping  the  blood  of  the  omphalo'iMSwaio  veins,  it  follows  that  both  expan- 
sion and  contraction  is  necessary  for  accomplishing  this,  the  one  for  aspirating 
this  fluid,  tin-  other  for  pn>|>ellini;  it.  This  would  explain  why  the  action  should 
In-ill  a  <il  this  r/(//(i////c  hi  urt.  ( )f  course,  as  the  area  of  circiilntioii  increases  it 
would  c.-Jl  for  corresjKMidmg  increase  of  force  for  effecting  it.  Accordingly,  prea- 
"I  for  facilitating  circulation  at  the  same  time  that  additional  force 
i>  placed  ii]x)ii  it  ;  notablv,  the  former  is  produced  \>\  tin1  ainniotic  fluid  and  the 
latter  by  the  action  in  the  ainnion. 

Tin'  aiuiiion  closes  around  the  embryo  of  the  chick  on  the  fourth  day, 
and  on  the  fifth  tluid  U^'ins  to  collect  in  the  sac,  and  by  the  seventh  the 
embryo  is  submerged  in  a  considerable  quantity  of  water.  "By  the  seventh 
day  very  obvious  movements  U'gin  to  api>ear  in  the  amnion  itself :  slow  vermic- 
ular contractions  creep  rhythmically  over  it.  The  amnion,  in  fact,  begins  to 
pulsate  slowly  and  rhythmically,  and  by  its  pulsations  the  embryo  is  rocked  to 
and  fro  in  the  egg.  This  pulsation  is  due,  probably,  to  the  contraction  of 
involuntary  muscular  fibres,  which  seem  to  be  present  in  the  attenuated 
jHirtion  of  the  mesoblast,  forming  part  of  the  ainniotic  fold"  (Foster  and 

K-llfoUM. 

The  physiological  significance  of  this  accumulation  of  amniotic  fluid,  and  the 
rhythmical  contractions  and  expansions  in  the  amnion,  may  not  be  doubted  for 
a  single  moment,  since  the  former  would  increase  pressure,  while  the  latter 
should  produce  the  necessary  changes  in  pressure  in  the  embryo  for  compelling 
respiration  and  circulation  to  be  in  correspondence  with  the  nutritive  and  func- 
tionid  processes  in  the  growing  chick,  both  of  which  are  constantly  extending 
their  limits  and  requiring  more  and  more  force  for  effecting  them.  These 
slow  pulsations  in  the  amuion  of  the  chick  answer  to  the  placental  and 
uterine  souffle  in  gestation,  the  principle  being  precisely  the  same.  How  other- 
wise explain  this  circumstance  ?  But,  as  has  already  been  remarked,  a II  pulsa- 
tion* relate  to  changes  in  pressure,  and  these  pulsations  in  the  amnion,  together 
with  the  amniotic  fluid,  relate  to  changes  in  pressure  in  the  embryo  for  increas- 
ing circulation  of  the  juices. 

The  explanation  of  the  mechanics  is  sufficiently  easy ;  notably,  there  are  two 
cardinal  points  from  which  to  regard  it — one  in  the  allantois,  the  other  in  the 
embryo.  First,  commencing  with  the  movement  of  expansion  in  the  allantois. 
The  increase  in  pressure  which  this  produces  in  the  embryo  through  the  am- 
niotic fluid  should  cause  the  venous  blood  to  flow  with  increased  energy  towards 
the  allantois,  the  point  of  low  pressure  within  the  egg  (the  heart  and  vascular 
>\ stem,  of  course,  assisting  in  this);  the  contraction  or  condensation  of  the 
amnion.  by  relieving  pressure  in  the  allantois,  enables  this  to  expand  part  passu 
with  contraction  in  the  amnion  for  aspirating  the  venous  blood,  at  the  same 
time  that  it  aspirates  the  air  through  the  outer  membrane  and  pores  of  the  shell. 
When  the  movement  is  reversed  by  expansion  of  the  amnion,  the  reduction  in 
pressure  which  this  effects  in  the  embryo,  together  with  the  simultaneous  in- 
crease of  pressure  it  produces  in  the  allantois  by  forcibly  compressing  this 
against  the  shell  wall,  causes  the  aerated  blood  in  the  latter  to  flow  with  aug- 
mented speed  into  the  heart  of  the  embryo,  as  also  through  the  tissues  of  the 


20 

1 'liter;  since  thet  blood  vascular  system  woiild  be  less  embarrassed  and  be  more 
free  to  act  in  cousequei:ce. 

.  |But  the  allantois  itself  also  participates  in   this  action,    the  fluid  it  contains 
enabling  it  to  effect  such  rhythmical  compression   of  the   capillary  plexuses 


TIG.    10. — DIAGRAM   OF   YOUNG  EMBRYO   AND    ITS   VESSELS,   showing  circulation   of  umbilical 
vesicles,  and  also  that  of  allantois,  beginning  to  be  formed.     (After  Ualtou.) 

(Fig.  10).  The  following  forcible  illustration  (Fig.  11)  by  the  distinguished 
biologistjat  Jena  will  serve  to  impress  the  matter.  At  this  early  stage  in  develop- 
ment (third  week  in  gestation),  it  will  be  seen  that  pressure  is  increased  at  the 
•cardinal  points,  namely,  vitellus  (a),  the  body  of  the  embryo  (c),  and  allantois 


FIG.    11.— HUMAN  EMBRYO  IN  THE   THIRD  WEEK.     A,   large  globular  yelk-sack;   f>,  allantois; 
c,  amnion ;  d,  tufted  cborion.     There  are  yet  limbs.     (After  llueckel.) 

(b).  As  the  embryo  and  allantois  are  elaborated  out  of  the  material  in  the 
vitellus,  this  would  explain  the  greater  accumulation  of  fluid  in  this  locality  for 
compelling  circulation  toward  those  two  points,  whilst  the  rhythmical  contrac- 
tions of  the  yelk  sac  should  greatly  expedite  it.  For  increasing  circulation 


•Jl 


between  tin-  cnibrvo  :uul  aliantois  (c,  /'i,  commensurate  pressure  is  prcxluced  by 
iici-iiinuliitiiHi  of  fluid  in  these  two  jitiints  or  jioles  of  tin-  circulation.  This,  to- 
gether witli  tin1  action  in  tin-  mtmihranes  themselves,  and  the  heart  and  vessels, 
is  siillicient  forcaiTvine;  on  circulation  in  the  iaitiul  stages  of  embryonic  evolu- 
tiou  ;  lnit  witli  tin-  incr.  "\\tli  comes  increasing  difficulty  for  effecting  it; 

hence  the  pumping  :ictii>n  whicli  is  set  up  in  the  placenta  and  womb,  together 
with  tin'  accumulation  of  iimiiiotic  lluid  for  transmitting  these  actions  upon  the 
embryo,  a.-  described  above.  Tlnis,  even  tiling  is  in  correspondence — the 
liquor  iimuii,  the  inoreaoBg  growth  of  tin-  placenta  .-mil  the  number  of  muscles 
and  nerves  in  the  walls  of  the  womb — and  so  continues  till  the  close  of  preg- 
nancy. In  other  \vonls,  it  all  forms  a  coniu-ctc d  whole  in  the  mechanics  of  the 
i-mhryoiiie  circulation. 

In  tlic  case  of  the  bird,  the  jillantois  answei-s  to  the  placenta,  since  it  pumps 
in  both  o\\L,'en  and  nutriment ;  only  that  the  pumping  action  in  the  abdomen 
(the  soft  hinder  parts  of  the  bird)  for  pumping  air  and  blood  through  the 
alveoli,  is  set  up  in  the  hitter  days  of  incubation,  when  rapid  atrophic  changes 
soon  obliterate  the  umbilical  vessels,  and,  breaking  the  now  attenuated  and 
fragile  sht  11-wall  witli  its  b«ak,  it  finally  makes  its  escape,  leaving  the  allantois 
and  atrophied  membranes  behind. 

MODE  OF  GRAFUMi    Till.   o\l\l    l\    THE   TISSUES   OF   THE   WOMB. 

In  jiHiiiiiH'iliii  tho  ovum  is  not  discharged  from  the  maternal  passages,  but  i« 
retained  in  the  expanded  oviducts  at  the  point  ol  juncture,  which  answers  to- 


FIG.    12.— A    VERTICU    Sn Tins    FROM    THE  FIG.    13.— Same  tubules,   greatly  magnified. 

UTERINE  Mi'cors  MEMBKAXK,  showing  the  (After  Dalton.) 

numbers  and    position    of    the    tubules. 
A,  free    surface  ;    6,    attached    surface. 

(After  Dalton.) 

the  womb,  where  growth  and  elaboration  are  effected  through  the  vascular  con- 
nections established  between  it  and  the  maternal  circulation.  Briefly,  the  mode 
of  closing  this  is  as  follows :  The  uterine  mucous  membrane  is  virtually  but  a 
dense  mass  of  single,  straight  follicles,  arranged  perpendicularly  to  the  free  sur- 
face (Figs.  12,  13),  and  with  the  closed  end  resting  against  the  muscular 


22 

walls  of  the  womb.  At  intervals,  fine  bloodvessels  course  up  between  them, 
and,  reaching  the  mucous  surface,  surround  the  tubules  with  a  capillary  network. 
But  when  fecundation  is  effected  vascular  turgessence  at  once  sets  in,  producing 
rapid  growth  and  development  of  the  membrane — of  the  follicles  especially  ; 
and,  coming  in  contact  with  this  highly  vascular  and  tumified  surface  as  it  leaves 
the  Fallopian  tube,  the  ovum  is  rapidly  incorporated  with  it,  by  means  of  the 
•shaggy  villosities  which  are  thrown  out  from  the  outer  surface  (Fig.  14,  «..), 


FIG.  14.— OVUM  OF  THE  RABBIT,  from  a  Graaflan  follicle  J6  of  an  inch  in  diameter.  A,  epithe- 
lium of  the  ovum;  6,  zona  pellucicla,  with  radiating  striations  (vitelline  membrane); 
c,  germinal  vesicle;  rf,  germinal  spot;  e,  vitellus.  (After  Waldeyer.) 

FIG.  15.— IMPREGNATED  UTERI'S,  showing  connection  between  villosities  of  chorion  and  decidual 
membranes.  (After  Dalton.) 

which  grow  into  the  expanded  orifices  of  the  tubules,  and  function  as  temporary 
villi  for  pumping  the  abundant  albuminous  secretions  of  the  glands  in  the  in- 
terior of  the  ovum.  Of  course,  they  contain  all  the  elements  of  tissue  struc- 
ture. With  the  ingrowing  of  the  shaggy  tufts  of  the  chorion  in  the  follicles, 
the  mucous  membrane  expands  around  the  ovum  for  bringing  the  follicles  in 
contact  with  every  portion  of  the  chorion  till  the  whole  is  completely  enclosed, 
forming  what  is  known  as  decidua  reflexa,  while  that  portion  of  the  membrane 
•with  which  it  first  came  in  contact,  in  immediate  relation  with  the  muscular 
walls,  constitutes  decidiia,  vera,  the  part  that  enters  the  structure  of  the 
placenta  which  is  subsequently  formed.  At  this  time  the  villosities  of  the 
chorion  project  into  the  uterine  follicles  in  every  direction  (Fig.  15),  but  as 
growth  proceeds,  aiirl  more  and  more  nutriment  is  needed  in  the  embryo,  the 
villi  in  relation  with  decidua  vera  become  vascular,  while  those  in  relation 
with  decidua  reflexa  are  atrophied,  in  consequence  of  which  this  portion  of  the 
•chorion  becomes  bald.  Finally,  the  transformations  which  occur  in  the  placenta 


' 


*   • 


convert  the  tubules  int..  pl.-iccnUl  sinuses,  and  tli.'  villi  of  the  chorion  into  vaa- 
culiir  loops,  •Demanded  and  embraced  liy  the  lining  membrane  of  the  HiiiUKOM, 
like  the  finders  of  a  glove  i  I'i^.  16),  aa  before  remarked;  hut  since  the  osipil- 

l.irv  lm>ps  ore  projected  ill  the  villi,  the  natural  inferenee  is  that  the  Walls  of   tllO 

latUT  coalesce  with  tin'  walls  of  the  sinuses  to  form  this  intervening  mem- 
brane. In  this  manner  the  embryonic  and  maternal  structures  are  inseparably 
Mended. 


!  1  .    I-,.     <KI  M   FROM  TIIK  MOLE.     A,  nucleus;  6.  cell  body;  c,  thickened  corpuscle  traversed  by 
pores.     (After  Leydig.) 

FIG.  ir.  TIIK  UIMVX  K.Ki  FROM  THE  OVARY  OK  TIIK  FKMAI.E:  MUCH  ENLARGED.  The  entire 
egg  is  a  simple,  globular  cell.  The  greater  part  of  the  spherical  egg-cell  is  formed  by  the 
egg-yelk,  or  the  granular  cell-sulwtance  (protoplasm),  which  is  composed  of  innumerable 
delicate  yelk  granules,  with  a  little  intervening  substance.  The  germ-vesicle,  answering  to 
tlif  .Til  kernel  (nucleus)  lies  in  the  upper  part  of  the  yelk.  It  contains  a  dark  nucleolns  or 
••ii-spoi.  Thi-^lolmlur  11111*4  of  yelk  is  surnmn<lr<l  l,y  u  thirk  transparent  egg-memlirane 
'«"'«  'I'liix  i-  penctraU'd  by  the  pore-canals,  in  the  form  of  very 

numerous  hair-like  lines,  which  run  rapidly  towards  the  centre  of  the  globe;  through  these 
the  thread-shaped,  moving  sperm  cells  pass,  in  the  process  of  impregnation,  into  the  egg-yelk. 

'Hie  common  relation  which  animal  life  sustains  to  the  organic  laws  has 

forcible  illustration  in  the  very  ova,  the  structure  being  fundamentally  the  same 

If.  and   17).      The  absence  of  a  shell  wall  permits  expansion  in  the 

chorion  /,-iri  ;>assu  with  the  growth  of  the  embryo,  while  the  womb  expands  in 

concert  with  this  action  in  the  chorion  and  embryo. 


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